Dynamic control systems for automotive vehicles have recently begun to be offered on various products. Dynamic control systems typically control the yaw of the vehicle by controlling the braking effort at various wheels of the vehicle. By regulating the amount of braking at each corner of the vehicle, the desired direction of the vehicle may be maintained.
Typically, the dynamic control systems do not address roll of the vehicle. For high profile vehicles in particular, it would be desirable to control the rollover characteristics of the vehicle to maintain the vehicle position with respect to the road. That is, it is desirable to maintain contact of each of the four tires of the vehicle on the road.
Vehicle rollover and tilt control (or body roll) are distinguishable dynamic characteristics. Tilt control maintains the body on a plane or nearly on a plane parallel to the road surface. Rollover control is used to maintain the vehicle wheels on the road surface.
In roll control systems, typically four-wheel speed sensors are used. The wheel speed sensors are used to determine the reference velocity of the vehicle. Because four-wheel sensors are used, each of the rear wheel speeds is known. In some systems, it may be desirable to reduce cost and not provide a separate wheel speed sensors, particularly for the rear wheels.
It would therefore be desirable to provide a system for determining a reference vehicle velocity and a rear-wheel velocity for each of the rear wheels from a system employing only three speed sensors.